<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *,html,body{
            margin: 0;
            padding: 0;
        }
        a{
            text-decoration: none;
        }
        ul,li{
            list-style: none;
        }
        

        .btn{
            font-size: 16px;
            color: chartreuse;
            background: #6761d6;
        }
        .btn:hover{
            font-size:30px;
            color: chocolate;
        }
        .btn:active{
            background-color: #d62525;
            color: aliceblue;
        }
    </style>
</head>
<body>
    <div class="container">
        <div>
            <span class="title">第二层级</span>
        </div>
        <span id="title" class="title">第一层级</span>

    </div>
    <a href="">百度</a>
    <ul>
        <li>111</li>
        <li>222</li>
        <li>333</li>
    </ul>
    <span class="title">456</span>
    <span>789</span>
    <button class="btn">点击变色</button>
</body>
</html>